Reading involves more than being able to look at a word and know how to say it aloud, either by sounding it out or being familiar enough to just know it. You must also be able to understand not only the meaning of the word but what it means in regards to the sentence around it. If your child is having trouble with reading comprehension, they will have trouble with all the other subjects at school. Talk with your child's teacher about a reading comprehension home program to help them learn to understand what they are reading. Here are a few of the things you can do with them to help.
Read a story to your child, breaking it down into paragraphs. After each paragraph, discuss it with your child. You do not need to go into detail, but discuss the main idea of it. Sometimes, shutting out the details in the beginning can help them to understand what is actually going on. At this point, it should be both of you talking about the meaning of the sentences. Then, tie all the sentences in the paragraph together.
After going over the main idea of a paragraph, ask them questions about it. You may have to read the passage again, so they can now pay attention to more details. Keep the main idea in mind and mention how it pertains to each question. Ask them who did what, where they did it, why, and how. You can even ask them to predict what may happen next. While discussing what your child is reading, discuss how some action caused something else to happen. You may also talk about how things are different or the same. If there is a problem, ask your child how they would solve it, and then talk about how it was solved in the story.
After your child reads a story or paragraph, ask them to tell you, in their own words, what it was about. In the beginning, they may have to retell each sentence before they will be able to tell you the whole story/paragraph. While it is okay to allow them to predict what may happen, it is important that anything from the story should be told as accurately as possible. Be sure the child understands the order of events in the story and any actions the character took to keep the story moving.
Reading comprehension is probably the most important skill your child needs to master. Without it, they cannot understand the other textbooks they read.